| The modulation technology(QAM) is widely used, and it is used not only in the mobile communication field, but also in other fields, such as wire television transmission field, Digital Video Broadcasting-Satellite communication(DVB-S)field, etc...The reason why QAM modulation technology gets so extensive applicable lies in its high frequency band utilization ratio. This is the modulation technology superiority in the mobile communication and satellite communication fields, in which the bandwidth resources are not so abundant.First of all, this paper introduce the basic principles of QAM modulation and demodulation, especially the base-band shaping theory of modulation and the carrier recovery theory of demodulation, then simulate the whole 16QAM modulation and demodulation system in the Matlab software's simulink toolbox. Beside research in theory, this thesis designs and built the key parts of 16QAM modulation and demodulation system based on FPGA with the simulation environment, which is constituted by the software of ISE9.1i and ModelSim6.1b. The key parts include the following modules:pseudo-random sequence generator, constellation mapping, base-band shaping filter, carrier signal generator, carrier recovery loop, constellation demapping. The srrc filter is used as base-band shaping filter,which is implemented by DA arithmetic,which achieveds the goal of total used resources redulation of the FPGA; we have adopted the use of CORDIC algorithm to replace the real-time computing sine look-up table in the DDS phase to achieve the conversion rate to overcome the use of DDS when ROM table phase truncation error; corrier recovery is implemented by costas loop,which is easy achieved.This paper achieve the simulation of the key modules of 16QAM modulation and demodulation system by the language of Verilog HDL in the simulation environment. The result of simulation and synthesis proves the correctness of the design. It laid the foundation of the next hardware design. |
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